I'm not sure I'd include the post office as a failure. If anyone honestly thinks that there's a private company out there who will deliver a letter to any address anywhere in the US for $.49, and to be able to do that while paying middle class wages and having the most overfunded pension in history I'd like some of whatever drugs they are taking.
But anyway, my point was simply that the government can, and has, done some pretty amazing large projects. Sure there have been failures. But to say that there haven't been major successes is simply not true.